Multiple access communications systems utilizing noise coded signals are well known. Typical examples of such multiple accessing communications systems are shown and described in: U.S. Pat. No. 3,908,088, entitled, "Time Division Multiple Access Communications System", which issued to Frank S. Gutleber, the present inventor, on Sept. 23, 1975; U.S. Pat. No. 4,215,244, entitled, "Self-Adaptive Mobile Subscriber Access System Employing Time Division Multiple Accessing", which issued to Frank S. Gutleber on July 29, 1980; and U.S. Pat. No. 4,301,530, entitled "Orthogonal Spread Spectrum Time Division Multiple Accessing Mobile Subscriber Access System", which issued to Frank S. Gutleber on Nov. 17, 1981.
What is significant about the systems disclosed in the aforementioned patents is that they employ pairs of multiplexed noise codes of the type termed code mates having autocorrelation functions which upon detection provide an impulse autocorrelation function and wherein the configurations described enable random access or direct call-up to be accomplished with minimal interference between users. The codes utilized are called noise codes because the information to be communicated is coded with a digital code that is "noise like" in that it will compress to an impulse when detected with a matched filter.
The utilization of different noise codes for a plurality of users in a nonsynchronous mobile subscriber multiple access system has been found to be heretofore less than adequate because of self-interference between users. Such a system is referred to as a non-orthogonal system. Although each interference signal is reduced by the time-bandwidth product, interfering users in close proximity make for intolerable system operation.